Is it rated over the same pulse duration? (I haven't compared the datasheets)
When you get down to it, its all a matter of how much energy the Silicon junction can absorb without either melting, or as the energy pulse dissipates, melting its die attach solder. The energy capacity will be almost directly proportional to the mass of silicon for short pulses. For longer pulses, the leadframe's ability to heatsink the die comes into play. If the Diotec part had a larger die area, but the die was thinner, it could easily have higher peak current handling capability, while still only handling the same pulse energy.
Alternatively Diotec may have been better at getting a uniform junction that resists 'hotspotting' which would cause local failure.